The present invention relates to a recoil starter mechanism for small internal combustion engines, for example, engines used on rotary lawnmowers.
Manual starting of a small internal combustion engine is frequently accomplished by a recoil pull-rope arrangement wherein a starting rope is coiled about a pulley and a starter gear arrangement is coupled to the pulley so that when the rope is pulled and unwound from the pulley, the pulley rotates and the starter gear arrangement is translated in one direction or another to engage a mating starter gear on the engine. A spiral spring associated with the pulley or starter gear arrangement rewinds the rope on the pulley when the handle is released. The translational movement of the starter gear out of engagement from the corresponding gear on the engine enables the engine to run freely without turning the recoil starting arrangement. In U.S. Pat. No. 4,019,490, there is disclosed a pulley and starter gear mechanism which translates in a direction generally perpendicular to their common axis of rotation to engage the gear associated with the pull-rope and a mating set of teeth on the engine flywheel.
Also known is a fixed axis pulley arrangement with a threaded hub member coupling the pulley and starter gear together so that initial rotation of the starter pulley urges the starter gear axially into engagement with mating teeth on the engine flywheel.
Centrifugally decoupled starting arrangements have also been employed wherein the engine flywheel or other rotating part of the engine carries one or more starter lugs spring biased to engage a ratchet wheel or pull-rope starter gear and, when the engine is started, the centrifugal force effect on the pawls moves them radially outwardly against the spring biasing and out of engagement with the starter ratchet wheel. Such lug type starter arrangements have enjoyed some commercial success, for example, in chain saws, but have not been as successful in more competitive markets of lawnmowers, snow throwers and similar applications due, at least in part, to the expense and complexity of assembly of the centrifugally actuated pawls.
Frequently, the small internal combustion engines to which the present invention applies employ a crankshaft driven flywheel having a series of vanes annularly disposed thereon for circulating air about the engine to cool the engine. Such an air circulating flywheel is frequently enclosed within a blower housing both for safety reasons and to appropriately duct the air about the engine for cooling purposes. The starter housing is often constructed as a separate part and is joined to the blower housing by fasteners, such as metal screws, for example. The use of a plurality of fasteners to connect the starter and blower housings results in increased assembly time.
The recoil spring is typically located within a chamber inside of the pulley or ratchet wheel, and the spring is often coated with an oil to prevent rusting and ensure smooth operation. A significant problem is the accumulation of dust on the oil coated recoil spring, because the accumulation of dust will begin to buildup between the coils of the spring thereby preventing the spring from being completely coiled when the rope is pulled. Dust build up also prevents the spring from completely recoiling when it is released so that the rope will not be completely retracted within the starter housing.